In a statement on its website, ZPS said: “We want to apologise sincerely to those affected, the survivors and their relatives, whose feelings we hurt.”

“In particular we want to apologise to the Jewish institutions, associations or individuals who feel that our work disturbed the peace required for the dead, according to the Jewish religion,” it said.

Image captionThe urn is the centrepiece of the art installation opposite the Reichstag

Historians say the Nazis killed about one million Jews at the vast Auschwitz-Birkenau camp complex, along with 300,000 others, most of them Poles and Soviet prisoners-of-war.

Chancellor Angela Merkel is to visit Auschwitz – in what was Nazi-occupied Poland – on Friday for the first time. She has previously visited Buchenwald and Dachau – two other notorious Nazi camps.

The Nazis murdered an estimated six million Jews at camps and mass execution sites.

Media captionAuschwitz: Drone footage from Nazi concentration camp

The ZPS statement expressed horror at the Nazi atrocities.

“Our work, our whole political and artistic activity, is driven by outrage at the Nazis’ crimes, whose goal was to deny their victims all dignity,” the statement said (in German).

The installation stands on a site opposite the Berlin Reichstag where, in March 1933, German MPs voted to give the Nazi dictatorship sweeping powers. At that time they met in the Kroll Opera House, which was demolished in 1951 because of severe war damage.

Image captionThe permanent Holocaust Memorial in the heart of Berlin

Josef Schuster, President of the Central Council of Jews in Germany, said that “from a Jewish perspective, the Centre for Political Beauty’s latest campaign is problematic because it violates Jewish religious law about not disturbing the dead”.

Speaking to Deutsche Welle, he said the group should have consulted a rabbi before taking the soil samples.

Charlotte Knobloch, another Jewish community leader in Germany, said the action “was meant to be provocative but is in fact only tasteless, tactless and irreverent”.

In 2017 the ZPS set up an imitation of Berlin’s Holocaust Memorial outside the house of far-right Alternative for Germany (AfD) politician Björn Höcke. He had earlier criticised the memorial as a “monument of shame” – triggering fears that he was trying to rehabilitate the Nazis.